[Bug 796519] Add AV1 codec parser

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=796519

--- Comment #14 from Georg Ottinger <g.ottinger at gmx.at> ---
> Please Correct me if I'm wrong,
> IIUC AV1 is it always packetized (one full frame in a buffer with all
> necessary OBUs in it). right? If so, why can't we do it similar to vp9? Only
> one API which accepts the input raw data and parse+fill all the necessary
> structures (sequece, frame etc) if the corresponding obus are present?
> 
> Or do you think it is possible to have the container formats to send only
> OBUs to the decoder instead of the whole frame (similar to H264 and HEVC)?

hmm, I am not 100% sure and I must admit that I don't fully understand the
packetized concept - but I can sum up what I think AV1 does:

AV1 is structured in 
1.) temporal units
2.) frame units
3.) OBUs

A temporal unit for example might look like this:

*Temporal Delimiter OBU
*Sequence Header OBU
*Frame OBU

it is marked by a "Temporal Delimiter OBU" and lasts before the next "Temporal
Delimiter OBU" starts.


but it can also look like this (for subsequent frames):

* Temporal Delimiter OBU
* Frame OBU

Note: all subsequent temporal units need the original Sequence Header
information in order to be decodeable.


A Frame OBU is basically the SUM of a Frame Header OBU and a Tile Group OBU
(minus one OBU header) and it is on its own a "frame unit"

But a frame unit might also look like this:
* Frame Header OBU
* 1st Tile Group OBU
* ...
* Xth Tile Group OBU

-> so there are a number of ways how temporal units and/or frame units might be
structured.

It might also be possible that within a temporal unit multiple frame units
reside.

Annex B for example additionally stores the information how much bytes the
actual temporal unit and also the frame unit(s) occupy. (in this case the size
of the "packet" is known) - but this is only for Annex B - in low overhead
bitstream format (the standard) this is not the case.

For example the output of dump_obu:

-----
$ ./dump_obu ~/SourceCode/aom_testdata/av1-1-b8-01-size-16x16.ivf
Temporal unit 0
  OBU type:        OBU_TEMPORAL_DELIMITER
      extension:   no
      length:      2
  OBU type:        OBU_SEQUENCE_HEADER
      extension:   no
      length:      12
  OBU type:        OBU_FRAME
      extension:   no
      length:      169
  TU size: 183
  OBU overhead:    3
Temporal unit 1
  OBU type:        OBU_TEMPORAL_DELIMITER
      extension:   no
      length:      2
  OBU type:        OBU_FRAME
      extension:   no
      length:      77
  TU size: 79
  OBU overhead:    2
File total OBU overhead: 5

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